JPH11140599A - Powder for sintered compact excellent in oxidation resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder for sintered compact having excellent oxidation resistance when used for automobile exhaust system parts. SOLUTION: The powder is composed of an austenitic stainless steel which has a composition containing, by weight, <=0.03% C, <=0.30% Mn, 9.5-21.5% Ni, 16.0-26.0% Cr, and <=3.0% Mo as base components, further containing >1-4% Si, and having the balance essentially Fe. Further, Nb is incorporated into the above composition by <=1 wt.%, if necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder for a sintered body having excellent oxidation resistance.

[0002]

2. Description of the Related Art In recent years,
Higher output and lower fuel consumption of automobile engines have progressed, and as a result, the temperature of exhaust gas has increased, and the characteristics required for materials for exhaust system parts of automobiles, especially oxidation resistance, have become severe.

[0003] Austenitic stainless steel SUS310S (melted material) is used as a material for exhaust system components of this type of automobile. However, the cost of exhaust system components made of this molten material is high. It has been studied to configure the united body.

[0004] When the exhaust system component is made of a powdered sintered body, the sintered body has a problem that its oxidation resistance is inferior to that of the ingot material due to the existence of many pores. Therefore, the composition of the sintered body or powder is simply SUS310S (melted material)
If the composition is merely the same as above, the oxidation resistance characteristics required for exhaust system parts cannot be satisfied.

[0005]

The invention of the present application has been made to solve such a problem. The powder for a sintered body according to claim 1 is, by weight%, C: ≦ 0.03%,
Mn: ≦ 0.30%, Ni: 9.5 to 21.5%, C
r: from 16.0 to 26.0%, Mo: ≤3.0%, from austenitic stainless steel further containing Si: more than 1% to 4% with the balance being substantially Fe It is characterized by comprising.

[0006] The powder for a sintered body according to claim 2 is, by weight%,
C: ≦ 0.03%, Mn: ≦ 0.30%, Ni: 19.
5 to 21.5%, Cr: 23.0 to 26.0%, Mo:
≦ 0.50% as a base component and further Si: more than 1%
It is characterized by being composed of an austenitic stainless steel containing 4%, with the balance being substantially Fe.

[0007] The powder for a sintered body according to the third aspect is the first or second aspect.
In any one of the above, Nb: wt%
It is characterized by containing 0%.

[0008] Here, the composition of the powder includes not only the case where the composition of each powder itself is the above composition, but also the case where the entire composition of the mixed powder is the above composition.

[0009]

The present inventors have studied the effects of adding various additives in order to improve the oxidation resistance of the powder sintered body. It has been found that oxidation resistance can be effectively improved.
However, the effect was obtained in the case of austenitic stainless steel powder, and no remarkable effect was obtained in ferritic stainless steel powder. The present invention has been made based on such knowledge.

Thus, it has been confirmed that when Si and Nb are contained in the austenitic stainless steel powder according to the present invention, a material satisfying the oxidation resistance required for exhaust system components can be obtained.

Next, the reasons for limiting each chemical component in the present invention will be described in detail. C: ≦ 0.03% When the C content exceeds 0.03%, the hardness of the powder increases, the green density decreases, and as a result, the sintered density also decreases. In addition, rust is easily generated also in terms of corrosion resistance. Therefore, C is 0.
03% or less.

Mn: ≦ 0.30% When the Mn content exceeds 0.3%, the oxygen content of the powder increases,
Since the moldability deteriorates, the content is set to 0.30% or less.

Ni: 9.5 to 21.5% If the Ni content is less than 9.5%, a martensitic structure appears in the powder, the powder becomes hard, and the compactibility and the compact density decrease. On the other hand, if it exceeds 21.5%, the powder cost increases, and since Ni is an austenite strengthening element, the sintering density is hardly increased (diffusion speed is reduced).

Cr: 16.0 to 26.0% If the Cr content is less than 16%, the oxidation resistance decreases (Fe
), And the amount of oxidation increases.) On the other hand, if Cr exceeds 26%, the powder becomes hard, the green density does not increase, and the density of the sintered body decreases.

Mo: ≦ 3.0% When the Mo amount is more than 3%, the oxidation weight increases, and the oxidation resistance decreases (molybdenum oxide having a low melting point is generated, which sublimates during firing to leave pores). .

Si: more than 1% to 4% (preferably more than 1% to
(3%) When the content of Si is more than 4%, the powder becomes hard, and the compressibility and the formability become extremely poor. Considering compressibility, 3% or less is desirable. On the other hand, if it is less than 1%, the oxidation weight increases, and the desired oxidation resistance cannot be obtained.

Nb: ≦ 1.0% (preferably 0.3 to
(0.5%) If Nb is more than 1%, the amount of oxygen in the powder increases, and the formability and sinterability deteriorate.

In the present invention, it is desirable that the Ni, Cr and Mo components be in the following amounts. The desirable amounts and reasons are described in detail below. Ni: 19.5 to 21.5% If the Ni content is less than 19.5%, the compressibility decreases. On the other hand, if it exceeds 21.5%, the cost and the sinterability are reduced.

Cr: 23.0 to 26.0% If the Cr content is less than 23%, oxidation resistance equivalent to SUS310S ingot cannot be obtained. On the other hand, if it is more than 26%, the powder hardens, and the compressibility decreases.

Mo: ≦ 0.50% If the Mo amount is more than 0.5%, the oxidation increase becomes large.

[0021]

Next, embodiments of the present invention will be described in detail. Table 1
Then, 1% of zinc stearate was added as a lubricant to powder having the composition and characteristics shown in Table 2, and the mixture was mixed with a blender for 30 minutes. Then, the mixed powder was compacted with an Amsler testing machine.

[0022]

[Table 1]

[0023]

[Table 2]

Next, this green compact was dewaxed (zinc destearate) at 500 ° C. for 30 minutes, and then sintered at each sintering temperature shown in Table 3 (holding time: 60 minutes). Table 4 shows the sintered density of the sintered body and the analysis values of C, N, and O together with the green density.

[0025]

[Table 3]

[0026]

[Table 4]

The sintered body was subjected to an oxidation test under the conditions of 850 ° C. × 100 hours (atmosphere furnace), and the oxidation resistance was evaluated by obtaining an increase in oxidation. The results are shown in Table 5 and FIG.

[0028]

[Table 5]

In Table 3, the reason why the molding pressure is different for each powder is that the density of the sintered body is almost the same (91 to 2).
%). In the case of a sintered body, the oxidation resistance is greatly affected by the sintering density. To examine the effect of the oxidation resistance due to the composition of each powder, here the sintering density is adjusted by adjusting the molding pressure. It is uniform.

As shown in Table 5 and the results of FIG.
In the case of ferritic stainless steel powder No. 8 (P434L-2Si), the effect of adding Si is not so much apparent as compared with No. 7, whereas austenitic stainless steel powder No. 2 (P316L -2Si-Nb), No.3 (P316L-3Si), No.
5 (P310L-2Si-Nb), No.6 (P310L-3Si), Si, Nb
That the oxidation resistance is effectively improved by the addition of
In particular, in the case of powders No. 5 and No. 6 having a composition equivalent to SUS310S, it can be seen that the increase in oxidation is suppressed to a low level by the addition of Si or the combined use of Si and Nb.

That is, in the case of SUS310S (melted material), the oxidation increase is 0.29, whereas
In the case of No. 5 and No. 6 having a considerable powder composition, Si, Nb
It can be seen that the addition reduces the oxidation increase to 0.14 to 0, which is lower than that of the ingot.

When the exhaust system component is made of a sintered body, the sintered density has a great influence on the oxidation resistance. In that sense, the density (relative density) of the sintered body is 90
% Is desirable.

Although the embodiment of the present invention has been described in detail, this is merely an example. The present invention is, for example, to mix powders having different compositions so that the composition as a whole of the mixed powder satisfies the required composition. For example, various modifications can be made without departing from the spirit of the invention.

[Brief description of the drawings]

FIG. 1 is a diagram showing an increase in oxidation of a sintered body using a powder of an example of the present invention in relation to a relative density.

Claims (3)

[Claims] C: ≦ 0.03% Mn: ≦ 0.30% Ni: 9.5 to 21.5% Cr: 16.0 to 26.0% Mo: ≦ 3.0% by weight% A powder for a sintered body having excellent oxidation resistance, comprising an austenitic stainless steel having a Si content of more than 1% to 4% as a base component and a balance of substantially Fe. 2. In% by weight, C: ≦ 0.03% Mn: ≦ 0.30% Ni: 19.5 to 21.5% Cr: 23.0 to 26.0% Mo: ≦ 0.50% A powder for a sintered body having excellent oxidation resistance, comprising an austenitic stainless steel having a Si content of more than 1% to 4% as a base component and a balance of substantially Fe. 3. The method according to claim 1, further comprising:
b. A powder for a sintered body having excellent oxidation resistance, characterized by containing Nb: ≦ 1.0% by weight.